1. Field of the Invention
The present invention relates to magneto-optic films, methods of preparing same and devices incorporating such films.
2. Description of the Prior Art
Magneto-optic films and/or various devices utilizing same have been described in the following patents, the teaching of which is incorporated herein by reference thereto: U.S. Pat. Nos. 4,500,173 and 4,500,177, directed to spatial light modulators. U.S. Pat. Nos. 4,625,167 and 4,755,752, directed to crack detection devices; U.S. Pat. No. 4,728,178, directed to switches, modulators; U.S. Pat. No. 4,604,577, directed to magnetic field sensors; and, U.S. Pat. Nos. 3,838,450; 3,989,352 and 4,608,742, directed to memory and recording/modulator devices. Magneto-optic films have also been used in optical isolators, see e.g., Fujitsu Science & Tech. Journal, Vo. 26, No. 26. Such films may also find utility in rotation sensors for brakes.
One of the drawbacks of monocrystalline ferrimagnetic oxide films has been the low coercivity (less than 1 Oe) of such films. See, e.g., Hansen et al. "Media for Erasable Magneto-optic Recording" IEEff Trans. Mag., Volume 25, pp. 4390-4404. . As an alternative to the low coercivity monocrystalline ferrimagnetic films the art has produced ferrimagnetic polycrystalline films. Such magneto-opt films have been prepared utilizing sputtering, vapor deposition or spray pyrolysis. However, such polycrystalline films have coercivity values of 200-2,000 Oe. These values are too high for the applications which the films of the present invention find utility, because of the high switch fields required.
The herein invention resides in the discovery that monocrystalline ferrimagnetic oxide films having good square shaped hysteresis loops of predetermined coercivity can be produced by imparting to such films defects of controlled size, number, and distribution. The present invention enables replicable production of monocrystalline ferrimagnetic oxide films which operate at low switch fields, The present invention now allows retention of the desirable properties of monocrystalline ferrimagnetic oxide films while modifying the low coercivity levels characteristic to such materials and providing a readily switchable film having a good square shaped hysteresis loop.